As semiconductor devices become faster and more highly integrated, the size of transistors continue to become smaller. When transistors become more integrated, a line of a semiconductor device becomes finer, leading to signals applied to the line typically being delayed or distorted. Thus, the operation speed of a semiconductor device is hindered.
Consequently, lines using copper are often used. Copper lines have lower resistance and higher electro-migration than lines formed of aluminum or an aluminum alloy. However, because copper is more expensive than aluminum, the fabrication cost increases when copper is used instead of aluminum. Also, regions of a semiconductor device adjacent to a copper interconnection line are often contaminated due to the migration of free copper electrons.
Thus, there exists a need in the art for an improved semiconductor device and fabrication method thereof.